1. Field of the Invention
The present invention relates to a wire dot printer, a wire dot printer head used for the wire dot printer and an armature used for the wire dot printer, and more particularly to a shape of the armature.
2. Discussion of the Background
There has been known a wire dot printer head wherein an armature with a printing wire coupled thereto is pivoted between a printing position and a stand-by position, and when the armature is pivoted to the printing position, a tip of the wire is brought into collision with a printing medium to effect printing. In a certain wire dot printer head of this type, there has been proposed a device wherein a magnetic flux is produced by a coil around the armature, that is to be pivoted, for forming a magnetic circuit that causes the armature to be attracted from a stand-by position to a printing position to effect printing.
The wire dot printer head of this type is required to pivot the armature at high speed between the printing position and the stand-by position with a recent increased printing speed. Therefore, weight saving of an armature, particularly a reduced thickness of an armature has been developed. However, performing a carburizing process to the weight-saved armature deteriorates durability at the joint section between a thick section and a thin section of the armature. In view of this, JPA Hei-4(1992)-169242 proposes that the thick section and the thin section of the armature are joined by a communicating section having a taper section or a curved surface section, thereby preventing the deterioration in durability of the armature due to the carburizing process. Further, the armature is composed of an arm that supports a wire and a magnetic circuit forming member that is provided at the arm for forming a magnetic circuit, wherein the arm and the magnetic circuit forming member are independently carburized, which prevents the deterioration in durability of the armature due to the carburizing process.
However, the armature is required to be violently pivoted as many as 2500 times per second between the printing position and the stand-by position with a recent increased printing speed. In this case, the armature disclosed in JPA Hei-4(1992)-169242 is damaged since stress is concentrated on the communicating section of the armature. This is because the thin section of the armature bends so as to be warped in the direction parallel to the wire, which causes stress to be concentrated at the upper and lower sections at the communicating section in the direction parallel to the wire. It should be noted that the communicating section is formed such that the thin section is made thick in its thickness direction (in the direction orthogonal to the wire), so that it is difficult to prevent the concentration of stress at the upper and lower sections at the communicating section in the direction parallel to the wire.
Even in case where an armature 100 is composed of an arm 102 supporting a wire 101 and a magnetic circuit forming member 103, the arm 102 bends so as to be warped in the direction parallel to the wire 101 as shown in FIG. 6, resulting in that stress 104 is concentrated at the upper and lower sections at the arm 102 positioned in the vicinity of the magnetic circuit forming member 103 in the direction parallel to the wire 101. This damages the arm 102 from the stressed section.